Add ErrorLogFormat directive for configuring the error log format, including

additional information that is logged once per connection or request.

Add error log IDs for connections and request to allow correlating error log
lines and the corresponding access log entry.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@992806 13f79535-47bb-0310-9956-ffa450edef68